Such countermasses, also known as reaction masses, comprise a charge of inert matter designed to balance momentum during firing, thereby eliminating recoil. To do this, a countermass is ejected backwards from the weapon by a propellant charge at the same time as a projectile is launched forwards.
The countermasses generally in use are constituted by solids that fragment on leaving the barrel of the weapon, which solids may be implemented, for example, in the form of a bundle of filaments of a plastics material.
A drawback presented by that type of countermass is that it gives rise to significant danger behind the weapon both for the person firing it and also for friendly troops.
Various solutions have been proposed for that problem. In particular the nature of the matter constituting the countermass has been optimized by reducing it to the form of a powder, granules, or the like.
However that requires the use of a container, as described in French patent FR-2 356 904.
The problem then arises of behind-weapon safety when the container bursts on leaving the barrel of the weapon.
There is also the problem of sealing between the piston that ejects the countermass and the barrel. When a shot is fired, the container, which is generally made of a prestressed material such as glass, breaks up into small pieces. These highly abrasive pieces of glass can become engaged between the piston and the barrel, thereby spoiling the sealing of the system and giving rise to leaks that are harmful to proper operation of the weapon.